It is common practice to manufacture exchangers for medical applications by following the general stages which follow:
The polyurethane-generating adhesive compositions used to prepare a seal in a medical exchanger generally comprise, before polymerization, one or more polyisocyanates, one or more polyols and, optionally, one or more polyfunctional crosslinking agents and/or one or more catalysts.
The polyurethane, once it is cured, has the essential function of forming a leaktight seal, in order for there to be no infiltration between the two compartments of the exchangers or with the outside. The risk of infiltration must in particular be avoided between the blood compartment and the dialysate compartment of medical exchangers for blood treatment. To achieve this, the polyurethane adhesive composition must exhibit satisfactory adhesion with the semi-permeable membranes of the exchangers, whatever the chemical nature of the materials of which they are composed. This composition must also exhibit satisfactory adhesion with the components of the exchangers with which it is brought into contact, such as the casing.
Another important quality required of exchangers for biomedical use is the biocompatibility of cured and sterilized polyurethane potting bodies, more especially their non-cytotoxicity. The stage of sterilization or of disinfection by an oxidizing process, in particular when it is a sterilization by irradiation, can render polyurethane cytotoxic.
Previously, in order to form non-cytotoxic potting bodies, various solutions were provided, thus: